Which of the following pairs of substances on reaction will not evolve gas?

1. Iron, and ${\mathrm{H}}_2{\mathrm{SO}}_4$ (aq)

2. Iron, and steam

3. Copper, and HCl(g)

4. Sodium, and ethyl alcohol

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Why does manganese show a maximum oxidation state of +4 in MnF₄ but reach +7 in Mn₂O₇?

The fusion of chromite ore (FeCr₂O₄) with Na₂CO₃ in air gives a yellow solution upon the addition of water. Subsequent treatment with H₂SO₄ produces an orange solution.

The yellow and orange colours, respectively, are due to the formation of:

1. Na₂CrO₄ and Na₂Cr₂O₇

2. Cr(OH)₃ and Na₂Cr₂O₇

3. Cr₂(CO₃)₃ and Fe₂(SO₄)₃

4. Cr(OH)₃ and Na₂CrO₄

At pH = X, \(\text{CrO}_4^{2-}\)​ (yellow) changes to \(\text{Cr}_2\text{O}_7^{2-}\) (orange), and vice versa at pH = Y.
What are the values of X and Y, respectively?

1. 6, and 8

2. 6, and 5

3. 8, and 6

4. 7, and 7

What is produced when excessive diluted nitric acid is combined with potassium chromate?

1. Cr₂O₇^2- and H₂O  

2. Cr³⁺ and Cr₂O₇^2-  

3. CrO₄^2-  

4. Cr₂O₄^2-  

The oxidation state of chromium in the final product formed by the reaction between KI and acidified potassium dichromate solution will be:

1. +2

2. +3

3. +4

4. +6

Which compound cannot decolourise KMnO₄ solution?

1. CO₃^-2

2. NO₂^-

3. S^2-

4. Cl^-

When neutral or faintly alkaline ${\mathrm{KMnO}}_4$ is treated with potassium iodide, the iodide ion is converted into 'X'. The formula of 'X' is:

1. ${\mathrm{I}}_2$

2. ${\mathrm{IO}}_4^{-}$

3. ${\mathrm{IO}}_3^{-}$

4. ${\mathrm{IO}}^{-}$

The reaction(s) involved in the preparation of potassium dichromate from iron chromite ore is/are: